1. Technical Field
The present invention relates generally to an improved method to manage logical volumes and, in particular, to a method and an apparatus for providing a logical disk in a logical volume management system. Still more particularly, the present invention provides a method and an apparatus to allow device management plug-ins in a logical volume management system.
2. Description of the Related Art
The Logical Volume Manager (LVM) is a subsystem for on-line disk storage management that adds an additional layer between the physical devices and the block I/O interface in the kernel of the operating system to allow a logical view on storage. For systems without an LVM, each of the partitions that is usable by the operating system is assigned a drive letter, such as “C:” or “F:”, producing a correlating drive letter for each partition on a disk in the computer system. The process which assigns these letters is commonly known.
For systems with an LVM, a drive letter may be mapped instead to a logical volume which may contain one or more partitions. The process by which partitions are combined into a single entity is known generically as “aggregation.”
There are various forms of aggregation, such as Drive Linking and software Redundant Array of Independent Disks (“RAID”). Each feature, i.e. a function that may be performed on a partition, aggregate or volume, offered by the LVM for use on a volume is a layer in the LVM. The input to a layer has the same form and structure as the output from a layer. The layers being used on a volume form a stack, and I/O requests are processed from the top most layer down the stack to the bottom most layer. Typically, the bottom most layer is a special layer called the Pass Through layer.
U.S. patent application Ser. No. 09/561,184, which is hereby incorporated by reference, discloses a multi-layer logical volume management system for an LVM in the OS/2 operating system. Similar systems can be extended to handle multiple levels of aggregation in other operating systems.
Currently, the OS/2 LVM uses OS/2 direct access storage device (OS2DASD) for a device manager. It is the only device manager that the OS/2 LVM uses. This limits the devices that the OS/2 LVM can be used with to those that OS2DASD can handle. Currently, OS2DASD will handle only local devices. Extensive modification would be required to handle network attached devices. Furthermore, revising OS2DASD for every new class of devices is expensive and dangerous as it raises the possibility of destabilizing existing code.
Therefore, it would be advantageous to have a method and an apparatus to enhance the logical volume management model to allow improved device manager support.